A few times i have run into this issue and i'm not sure of an automatic way of correcting it.

An email comes in and gets greylisted. 5 or so minutes later the sending server honors the request and sends the email again, however it then comes from a different IP address. How can i have greylist automatically honor this message and have it approved to be delivered to the employees mailbox?

As of now, i either have to wait for this endless loop to finally use an IP a second time, or i have to go in and configure the clients_fqdn_whitelist or clients_ip_whitelist to allow the emails through without future filtering.